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Garage fumes drawn into house

user-917907 | Posted in General Questions on

I am planning a small air-tight house, which I was thinking of ventilating with an exhaust-only system. However, I also want an attached garage. I’m concerned that the negative pressure in the house may draw unwanted fumes in from the garage. Are there any recommendations for supplying make-up air to the house so that there isn’t negative pressure in the house, or perhaps a well-sealed door between the house and the garage? Any other ideas, besides a HRV system or a detached garage?

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  1. 3R3RyaN4Uo | | #1

    I've been using the humidity sensing intakes for several years with very good results.

  2. 3R3RyaN4Uo | | #2

    Seattle code requires a fresh air intake of some sorts in each of the bedrooms.

  3. jklingel | | #3

    If possible, install a big cfm fan that goes on whenever the garage door is opened. Let it run about 20 minutes thereafter, using fresh air make up specifically for the garage. Also, have your people door to the garage open into the garage so any neg pressure in the house tends to draw the door closed.

  4. GBA Editor
    Martin Holladay | | #4

    If it's not too late, consider a detached garage. Even a garage connected by a short breezeway is safer than an attached garage.

  5. user-917907 | | #5

    Thank you, Peter, for suggesting an occupant-sensing ventilation system. Can anyone else who's used the Conservation Technology system recommend it?

    John, good idea about the ventilation fan and having the door swing into the garage.

    Martin, you must feel strongly in favor of a detached garage. I really like the idea of the garage and the house sheltering and warming each other, and the sharing of the common wall means less foundation, framing, roofing and cladding. Sure would like to find a way to have my cake and eat it too.

  6. toymaker | | #6


    I built my home with a long tandem attached garage along nearly all the cold northern exposure, with attic above. The savings in materials and energy help to green the whole, if having a garage at all can really be considered green. I also turn off my Prius when its in the garage so any fumes are very temporary and certainly don't approach dangerous levels. The garage is totally sealed from the living space, 5/8 fire-rated drywall, fireproof steel entry door, etc.

    On the other hand if you are a fan of remote starting cars I'd go with a carport. If your memory is like mine you might start it and forget it. My CRS* syndrome is getting worse every year.

    *CRS (can't remember sh**)

  7. kevin_in_denver | | #7

    I've found that with our hybrid car we can back out and close the overhead door before the gas engine ever kicks on.

  8. user-869687 | | #8

    Prius? Come on people, you're not trying hard enough.

  9. homedesign | | #9

    It amuses me how many people have such strong feelings about their attached Garages and or Basements.
    I thought Martin was kidding when he justified his basement with his "bucket of drywall mud" reasoning.

    Looking at one of Thorsten's Photos from Alaska....
    It seems that Thorsten's homes do not have attached Garages or Basements
    Sure enough...there it is...... THE BUCKET OF MUD

  10. user-917907 | | #10

    The savings in materials and energy help to green the whole, if having a garage at all can really be considered green.

    Green? Whose talking green? I'm mostly interested in avoiding white -- as in white fingers when working on my car in the winter! ;)

  11. GBA Editor
    Martin Holladay | | #11

    Completely serious. I need a basement for my mud.

  12. user-659915 | | #12

    "I'm mostly interested in avoiding white -- as in white fingers when working on my car in the winter! ;)"

    I sympathize - up too a point - but it doesn't sound very smart or effective to rely on leakage from the house through an inadequately insulated common wall to heat your garage. It's only leaky homes that have made attached garages an acceptable arrangement. Tight homes demand a different standard.

  13. jklingel | | #13

    Some of Thorsten's homes have attached garages, but I don't know if these are older models, or current stock. See After 37 years up here w/ neither an attached garage nor an HRV, the new house will have both. The garage may end up being cold storage, but I think we'll be fine if we pay attention. James M: I would guess that tight homes w/ HRV's would be less likely to get nasty gasses in them than drafty homes. No?

  14. user-917907 | | #14

    James, I don't plan to rely on heat leaking from the house to heat the garage. The garage will be cold unless I specifically heat it, just not as cold as it would be with four walls exposed to the weather, instead of three walls. Likewise, one wall of the house will be warmer because it will be buffered by the garage.

    John, it sounds like a very good idea to use 5/8" sheetrock in the garage, and a steel fire-rated door between the garage and house. I've never heard of a tandem garage. Do you have a garage door at each end?

  15. HDendy | | #15

    A passive air inlet somewhere in the house- an easier path for incoming air than leakage from the garage. Better to know where the air is coming in, even if it's not from the garage. A well sealed door between the garage and the house is not just a good idea- it's required by code.

    edit for product info: I'm sure there are plenty of mfgr's of passive air inlets, one that I have bookmarked (not affiliated with) is American Aldes. Ask your HVAC contractor for recommendations too.

  16. Daniel Morrison | | #16

    There are some details for this connection in the Energy Star Air Sealing page, sections 1.2 and 3.1 specifically.

  17. Coyo | | #17

    John is correct - I am not a fan of crawlspaces or even worse attached garages. I build plenty in my career and have been ignorant about their problems until I started to educate myself. Email me if you like more information; I have a write-up "Sealing Garage spaces in our homes" which goes into this problem and offers some solutions.

    In a nutshell: Garage spaces in homes introduce deadly pollutants: Hydrocarbons in form of Benzene and Carbon monoxide.

    The only way to keep any of these dangerous pollutants out of your house it to detach your garage from your living quarters. If this is not an option, I highly recommend that you educate yourself about the long term health effects from exposure of these pollutants on our human bodies. A lot of research has been done and can be goggled. Once you understand the problem the steps to take to minimize risk of exposure will not seem so excessive anymore and make more sense. There are really no shortcuts to take...they don't work.

    • Meticulous air sealing of any adjoining walls and ceilings from the garage to the living space
    • Minimized penetrations with the adjoining spaces (no electrical panel etc)
    • Air tight door installed swinging into the garage, ensuring a good seal once the house part goes negative (kitchen exhaust etc)
    • Before the walls are closed air sealing needs to be tested for leakage with a depressurization test (blower door)
    • Garage space requires a dedicated exhaust system which is actively ventilated and activated with a motion sensor and is also tied into the garage door opener.

    Fresh air is a necessity for all life and good air quality is imperative for our well-being.

    PS: Pls ignore my ridiculously outdated web page which has not seen an update in over 6 years. One of these days...

  18. user-917907 | | #18

    Thorsten, here I go hijacking my own thread, but I was wondering why you don't like crawlspaces? Is it just because they are difficult for a builder to work in? Or is there a problem with them unique to your cold climate? Or something more fundamental?

  19. Coyo | | #19

    Jack, now why don't I like Crawlspaces? You're talking to the Guy who looks and studies the heat loss and thermal bridging from plumbing stacks though roofs and foundations...
    They are an incredible energy hog and often times on top of that a source of many bad pollutants, heated conditioned space which is never really utilized, expensive to build, expensive to maintain and bad for your indoor air quality. In my opinion they are fundamentally just wrong and should be avoided altogether.

  20. squibt | | #20

    Completely serious. I need a basement for my mud.
    Posted Mon, 03/14/2011 - 20:46

    Common could have built a mud room instead of a much mud does a person need? 8-)'

  21. GBA Editor
    Martin Holladay | | #21

    I have a mudroom, and I'm glad I have it. It's for mud from my boots, not for sheetrock mud. It's on the north side of my house, and it freezes, so the sheetrock mud goes in my basement.

    When it's 20 or 30 degrees below zero, mudrooms freeze, unless you want to dump heat into them. I don't.

  22. squibt | | #22

    Just jerking your chain on words..."mud room"

  23. homedesign | | #23

    you did not exactly answer Tim's question
    "How much Mud does a person Need?"

    I would say the average person may not need to store "much" mud.

    How much do you need to store and what do you use it for?

    Have you thought about buying it in powder form and adding water as needed?

  24. squibt | | #24

    I think he hoards mud....

  25. user-917907 | | #25

    ...You're talking to the Guy who looks and studies the heat loss and thermal bridging from plumbing stacks though roofs and foundations...
    Answered by Thorsten Chlupp

    Thorsten, if you're that concerned with thermal bridging from plumbing stacks then you must certainly be concerned with how smoke pipes/chimneys penetrate a ceiling and roof. What are the best methods you've found to seal the pipe and limit heat loss through conduction of the chimney material and convection of warm air up the chimney?

  26. u5XaeYJGMY | | #26

    Jack - Please consider cheap Central Fan Integrated Supply ventilation. I also posted to the April 4th article.

    Jack, I am so glad you are asking about the make-up air side of ventilation too. I’m glad to share my solution. I wanted to get controlled fresh air 24x7 plus slightly positive air pressure to help with indoor air quality. Along the way I learned that HRVs do not add supply make-up air – they only replace what they take out. I found this GBA article was very helpful: “Designing a Good Ventilation System: Ventilating Is Easy — It’s Ventilating Right That’s Hard (Musings of an Energy Nerd, Martin Holladay, June 15 2010). It helped me validate a decision to use Central Fan Integrated Supply (CFIS – my abbreviation) for my very tight and efficient house. I found very good information plus cold and warm region CFIS approaches from Building Science Corporation ( GBA staff collaborates with BSC staff to provide super well-reasoned advice. Check out RR-0304: Central Fan Integrated Supply Ventilation—The Basics. There’s additional articles from there – the BSC search bar works well. I chose the Aprilaire 8126 ventilation controller/damper integrated with an Aprilaire dehumidifier, but there are other installation options. For apples-to-apples comparison, the 8126 is $100+ and installation of insulated ductwork and integration into my HVAC was an additional $300 (in Sept 2010) for my new home. CFIS brings fresh air into your return air plenum for mixing by your existing HVAC system. An important requirement is a high-efficiency ECM variable speed blower on your furnace. Make sure your heater choice has an efficient exhaust blower motor too, since both are running when venting, heating or cooling. Ventilation demand calls have to be calculated and programmed via your thermostat or other HVAC control method. I may find that I still want an HRV in the future. But for now I am very happy with a thermostat setting of 70 F and initial natural gas bills of $66 in January and February 2011 in Cleveland (for heating 3400 SF first, second, and basement plus gas cooking, and gas dryer).

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